Insects that require blood for reproduction (e.g. mosquitoes) and/or for further development during at least a portion of their life-cycle (e.g. fleas and ticks), are not only an annoyance to humans and animals, they are often the vectors of seriously debilitating and potentially fatal diseases to both humans and animals alike.
For example, tick-borne illnesses suffered by a host can result from infections by numerous types of pathogens, including bacteria, viruses, and protozoa. Because ticks can carry more than one type of pathogen simultaneously, hosts can actually be infected with more than one pathogen at the same time. This can make diagnosis and treatment even more complex. Notable tick-borne diseases include lyme disease, Rocky Mountain spotted fever, relapsing fever, tularemia, tick-borne meningoencephalitis, Colorado tick fever, Crimean-Congo hemorrhagic fever, babesiosis, cytauxzoonosis, ehrlichiosis, anaplasma, ehrlichia canis and candidatus neoehrlichia mikurensis. Tick bites can even create an allergy to red meat in some people, due to the allergen galactose alpha-1, 3-galactose.
Fleas can transmit a tapeworm called dipylidium caninum haemobartonellosis which affects red blood cells, another parasite called dipetalonema reconditum, plague caused by yersinia pestis, typhus caused by rickettsia typhi and rickettsia felis, tularemia caused by francisella tularensis and bartonella henselae, myxomatosis, the hymenolepiasis tapeworm, and trypanosome protozoans.
Mosquitoes in the United States can carry eastern equine encephalitis, western equine encephalitis, St. Louis encephalitis, La Crosse (LAC) encephalitis, West Nile Virus encephalitis, Dirofilaria immitis (heartworm), and sometimes even malaria.
Ticks are particularly insidious because they can spread disease while feeding during any of their life-cycle stages, which include their larva, nymph and adult stages. Ticks typically acquire the disease causing pathogens while feeding on the blood of an infected animal. This typically occurs during their nymph stage when they are more likely to feed on small disease-carrying animals such as rodents and birds. However, tick eggs can even become infected with pathogens inside of the ovaries of the adult female, meaning that baby ticks in the larva stage can be infectious immediately at birth and before feeding on their first host.
Ticks are particularly small when in the larva and nymph stages of their development, and this can make their presence very difficult to detect. They are also able to secrete small amounts of saliva with anesthetic properties so that the animal or person that is to serve as its host can't readily feel that the tick has broken the skin and has attached itself for a meal. Thus, they can often go unnoticed until they have completed their feeding, which can take up to several days.
The risk of acquiring a pathogen from a feeding tick increases commensurately with the amount the tick is allowed to feed. This is because as the tick completes its feeding, it tends to regurgitate some of its meal before releasing its grip on its host. This permits the back-flow of blood into the bloodstream of its host, which can include the pathogens. It is important to note that ticks can potentially be stimulated into disgorging some of their blood meal when they are disturbed during feeding. This can occur if the tick is squeezed or otherwise aggravated during an attempt to remove the tick, or in the presence of known formulations of repellents that the tick finds disturbing.
Thus, it is highly preferable that ticks, once attached and feeding, be removed as quickly and carefully as possible. It is critical that this be done without squeezing or otherwise disturbing or aggravating the tick into disgorging part of its meal, as this can greatly increase the possibility of being infected. Removing ticks while avoiding disturbing them can be extremely difficult, and preferably requires special tools to ensure that the tick is completely removed without leaving mouth parts embedded in the skin.
Clearly, the best way to thwart the spread of diseases from these insects is to discourage them from biting in the first place. For mosquitoes, this can be accomplished by using an effective repellent applied to the skin and/or clothing. Compositions based on the chemical known as DEET (N, N-diethyl-m-toluamide) can be applied to exposed skin for protection that lasts up to several hours. While DEET has been shown to be quite effective in repelling mosquitoes, its effectiveness in repelling ticks has not been well-demonstrated. Moreover, ticks are known to wander over the body of a potential host until one finds a suitable spot, perhaps where DEET has not been applied such as under clothing, or where it has worn off. The use of chemicals is often less than desirable. They can cause irritation to the skin of both humans and animals. DEET can also cause degradation of plastics and other synthetic materials because it is a fairly strong solvent.
A plethora of chemical-based flea and tick baths have also been developed and marketed that are designed to interfere with the brains and overall neurological systems of those insects, ultimately causing their death. Unfortunately, most of these products can also affect the neurological systems of animals and humans coming into contact therewith. Many of these chemicals are known carcinogens. For example, phenothrin (85.7%) in combination with methoprene was a popular topical flea/tick therapy for felines. Phenothrin kills adult fleas and ticks. Methoprene is an insect growth regulator that interrupts the insect's life cycle by killing the eggs. However, the U.S. Environmental Protection Agency required at least one manufacturer of these products to withdraw some products and has required strong cautionary statements to warn of adverse reactions on others.
A number of repellent/insecticide products have also been formulated using natural ingredients such as plant essential oils. A number of plant essential oils have demonstrated repellent properties on insects because the insects simply do not like how they smell. For example, lemon eucalyptus has reasonable repellent properties against mosquitoes. Citronella has been used in candles as a reasonably effective repellent. Fleas and ticks do not like the aroma of neem oil, cedarwood or cedar oil, and garlic. Peppermint oil, clove extract, neem oil, have also been shown to repel fleas and ticks, and can even kill them in the right concentrations.
One of the downsides to repellent/insecticide products made of plant essential oils is that they can be irritating to the skin of humans and animals alike. For example, when provided as a spray for application to the skin, they are typically diluted in water and are quite acidic in nature. The pH of such formulations can often be in the range of pH=3-4. When created as a soap or shampoo, the acidic nature of the essential oils are typically overwhelmed by the basic nature of the soap formulation and the pH of such formulations can be highly basic, in the range of pH=7.5 to 9. Thus, both of these product types as currently available on the market have a pH that is inadequate for effectiveness as a repellent/insecticidal, and that is poorly tolerated on the skin of humans and animals.
Another problem that is not well-addressed by currently available repellent/insecticides made from plant essential oils is that ticks can be aggravated by the application of such formulations once they are attached and feeding from a host. This can cause them to burrow into the skin even harder because they are not happy with the new environment created by applying the spray or soap, and may want to resist being extracted from the skin. Moreover, even if the applied formulation ultimately results in the tick's demise, as discussed above, it can potentially cause it to regurgitate some of its meal, thereby increasing the potential of spreading a disease from the tick.